Control apparatus for internal combustion engine

ABSTRACT

A control apparatus for an internal combustion engine that varies the amount of lift of an intake valve is disclosed. In one embodiment, the control apparatus includes a fuel injection timing correcting device that, when lift of the intake valve is varied, corrects and varies fuel injection termination timing according to the variation of the lift of the intake valve. In another embodiment, an injection quantity correcting device is included that, when lift of the intake valve is varied, corrects and varies an injection quantity. In still another embodiment, a swirl flow generating device is included that generates a swirl flow in the cylinder. In a further embodiment, an intake valve closing timing correcting device is included that, when lift of the intake valve is varied, controls the variable valve timing mechanism so that the valve closing timing of the intake valve remains substantially constant.

CROSS REFERENCE TO RELATED APPLICATION

The following is based on and claims priority to Japanese PatentApplication No. 2005-264566, filed Sep. 13, 2005, which is incorporatedherein by reference.

FIELD

The present invention relates to a control apparatus for an internalcombustion engine that varies the amount of lift of an intake valve.

BACKGROUND

Internal combustion engines have been proposed that include a variableintake valve lifter that varies the amount of lift of an intake valve.An example of this type of variable intake valve lifter is disclosed inJapanese Patent No. 2827768. Specifically, the control mode of thevariable intake valve lifter is switched between low lift mode and highlift mode in accordance with the state of operation of the internalcombustion engine. In low lift mode, a cam for driving andopening/closing an intake valve is changed to a cam for low lift toreduce the amount of lift of the intake valve. In high lift mode, thecam for driving and opening/closing the intake valve is changed to a camfor high lift to increase the amount of lift of the intake valve.Accordingly, the variable intake valve lifter varies the amount of liftof the intake valve by switching between low lift mode and high liftmode.

Such systems can pose certain problems. For instance, from the intakestroke to the initial stage of the compression stroke, rich gas (i.e., afuel-air mixture rich with fuel) can be disproportionately distributednear the intake ports in the cylinder. This phenomenon is illustrated inFIG. 10, wherein the variable intake valve lifter is switched from lowlift mode to high lift mode (i.e., when the amount of lift of an intakevalve is increased). As shown, when the valve closing timing of theintake valve is delayed from Bottom Dead Center (labeled “BDC” in FIG.10) at this time, the intake valve remains open until the initial stageof the compression stroke. For this reason, back flow may occur, and therich gas disproportionately distributed in proximity to the intake portsin the cylinder in the initial stage of the compression stroke may bepushed back toward the intake port. As a result, the average air-fuelratio in the cylinder may be detected as being lean. Thus, immediatelyafter the mode is switched from low lift mode to high lift mode, a leanspike can occur as illustrated in FIG. 11. In other words, the averageair-fuel ratio in the cylinder temporarily fluctuates toward lean.

In the second and following cycles after switching to high lift mode,rich gas that flowed back to intake port in the compression stroke ofthe previous cycle is re-introduced into the cylinder as illustrated inFIG. 10. As a result, the average air-fuel ratio in the cylinder isapproximately equal to a target air-fuel ratio.

However, when the mode is thereafter switched from high lift mode to lowlift mode (i.e., when the amount of lift of the intake valve isreduced), a phenomenon occurs as illustrated in FIG. 12. Specifically,when the valve closing timing of the intake valve is returned toapproximately the BDC, the back flow of rich gas in the cylindersubstantially stops. For this reason, the residual volume of rich gas inthe cylinder is increased, and the average air-fuel ratio in thecylinder becomes rich. As a result, immediately after the mode isswitched from high lift mode to low lift mode, a rich spike occurs asillustrated in FIG. 13. In other words, the average air-fuel ratio inthe cylinder temporarily fluctuates toward rich.

More specific description will be given. During the period from theintake stroke to the initial stage of the compression stroke, theair-fuel ratio distribution of the fuel mixture in the cylinder is notuniform. Rich gas is disproportionately distributed in proximity to theintake ports in the cylinder. Therefore, when the valve closing timingof an intake valve is changed by varying the amount of lift of theintake valve by a variable intake valve lifter, the back flow of richgas disproportionately distributed in proximity to the intake ports inthe cylinder is increased or reduced. A lean spike or a rich spikeoccurs. This lean spike or rich spike can cause torque shock, which canlead to degraded drivability or deteriorated exhaust emission.

SUMMARY OF THE INVENTION

A control apparatus is disclosed for an internal combustion engine thatvaries the amount of lift of an intake valve. The control apparatusincludes a fuel injection timing correcting device that, when the amountof lift of the intake valve is varied, corrects and varies fuelinjection termination timing according to the variation of the lift ofthe intake valve.

A control apparatus is also disclosed for an internal combustion enginethat varies the amount of lift of an intake valve for a cylinder. Thecontrol apparatus includes a swirl flow generating device that generatesa swirl flow in the cylinder.

A control apparatus is further disclosed for an internal combustionengine. The internal combustion engine is equipped with a variableintake valve lifter that varies the amount of lift of an intake valveand a variable valve timing mechanism that varies the opening/closingtiming of the intake valve. The control apparatus includes an intakevalve closing timing correcting device that, when the amount of lift ofthe intake valve is varied by the variable intake valve lifter, controlsthe variable valve timing mechanism so that the valve closing timing ofthe intake valve remains substantially constant.

A control apparatus is still further disclosed for an internalcombustion engine that varies the amount of lift of an intake valve. Thecontrol apparatus includes an injection quantity correcting device that,when the amount of lift of the intake valve is varied, corrects andvaries an injection quantity.

A method of controlling fuel injection timing is additionally disclosedfor an internal combustion engine that varies the amount of lift of anintake valve. The method includes correcting and varying fuel injectiontermination timing according to the variation of the lift of the intakevalve when the amount of lift of the intake valve is varied.

Also, a method of controlling opening/closing timing of an intake valveof an internal combustion engine is disclosed. The internal combustionengine is equipped with a variable intake valve lifter that varies theamount of lift of an intake valve and a variable valve timing mechanismthat varies the opening/closing timing of the intake valve. The methodincludes controlling the variable valve timing mechanism so that thevalve closing timing of the intake valve remains substantially constantwhen the amount of lift of the intake valve is varied by the variableintake valve lifter.

Moreover, a method of controlling an injection quantity of an intakevalve is disclosed for an internal combustion engine that varies theamount of lift of the intake valve. The method includes correcting andvarying an injection quantity when the amount of lift of the intakevalve is varied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of an engine control systemwith a variable intake valve lifter;

FIG. 2 is a valve lift characteristic diagram for explaining the valvelift characteristic of a variable intake valve lifter in low lift mode;

FIG. 3 is a valve lift characteristic diagram for explaining the valvelift characteristic of a variable intake valve lifter in high lift mode;

FIG. 4 is a flowchart illustrating one embodiment of a fuel injectiontiming computation program;

FIG. 5 is a flowchart illustrating one embodiment of an injectionquantity computation program;

FIG. 6 is a plan view illustrating one embodiment of a swirl valve;

FIG. 7 is a flowchart illustrating one embodiment of a swirl valvecontrol program;

FIG. 8 is a valve lift characteristic diagram for explaining oneembodiment of a method for switching from low lift mode to high liftmode;

FIG. 9 is a valve lift characteristic diagram for explaining the methodfor switching from high lift mode to low lift mode in embodiment of FIG.8;

FIG. 10 is a valve lift characteristic diagram for explaining aconventional system for switching from low lift mode to high lift mode;

FIG. 11 is a time diagram illustrating air-fuel ratio behavior for thesystem of FIG. 10;

FIG. 12 is a valve lift characteristic diagram for explaining aconventional system for switching from high lift mode to low lift mode;and

FIG. 13 is a time diagram illustrating air-fuel ratio behavior for thesystem of FIG. 12.

DETAILED DESCRIPTION

Hereafter, description will be given to various embodiments of theinvention.

First Embodiment

Description will be given to the first embodiment of the invention withreference to FIG. 1 to FIG. 4.

First, description will be given to the general configuration of anengine control system with reference to FIG. 1. An air cleaner 13 isprovided at the most upstream portion of the intake pipe 12 of aninternal combustion engine 11. An air flow meter 14 that detects thequantity of intake air is provided downstream of this air cleaner 13.Downstream of this air flow meter 14, there are provided a throttlevalve 16 and a throttle angle sensor 17. The angle of the throttle valve16 is adjusted by a motor 15 (e.g., a DC motor), and the throttle anglesensor 17 detects the angle of the throttle valve 16.

A surge tank 18 is provided downstream of the throttle valve 16, andthis surge tank 18 is provided with an intake manifold pressure sensor19 that detects intake manifold pressure. The surge tank 18 is providedwith an intake manifold 20 that guides air into each cylinder of theengine 11. A fuel injection valve 21 for injecting fuel is installed inproximity to the intake ports of each cylinder in the intake manifold20. Spark plugs 22 for respective cylinders are installed in thecylinder head of the engine 11. The air-fuel mixture injected into thecylinders is ignited by spark discharge from the respective spark plug22.

The intake valves 29 of the engine 11 are provided with a variableintake valve lifter 30 that varies the amount of lift of the intakevalves 29. The variable intake valve lifters 30 can be switched betweenlow lift mode and high lift mode. In low lift mode, as illustrated inFIG. 2, the variable intake valve lifter 30 operates a cam for drivingand opening/closing the intake valve 29 for low lift of the intake valve29. As such, the variable intake valve lifter 30 reduces the amount oflift of the intake valve 29 and reduces a valve opening duration (i.e.,the amount of time that the intake valve 29 is open is reduced). In highlift mode, as illustrated in FIG. 3, the variable intake valve lifter 30operates a cam for driving and opening/closing the intake valve 29 forhigher lift of the intake valve 29. As such, the amount of lift of theintake valve 29 is increased, and the valve opening duration isincreased (i.e., the amount of time that the intake valve is open isincreased).

As illustrated in FIG. 1, a catalyst 24 (e.g., a three way catalyst) isprovided in the exhaust pipe 23 of the engine 11 for purifying exhaustgas and reducing CO, HC, NOx, and the like therein. An exhaust gassensor 25 (e.g., an air-fuel ratio sensor, oxygen sensor, or the like)is provided upstream of the catalyst 24 for detecting the air-fuel ratioof exhaust gas, whether the mixture is rich/lean, or the like.

In the cylinder block of the engine 11, there are installed a coolingwater temperature sensor 26 and a crank angle sensor 27. The coolingwater temperature sensor 26 detects cooling water temperature, and thecrank angle sensor 27 outputs a pulse signal each time the crank shaftof the engine 11 rotates through a predetermined crank angle. Based onthe output signal of the crank angle sensor 27, a crank angle and thenumber of engine revolutions are detected.

The output of these sensors are inputted to an engine control unit 28(hereafter, referred to as “ECU”). In one embodiment, the ECU 28 is amicrocomputer that executes various engine control programs stored in abuilt-in ROM (i.e., storage media). The ECU 28 thereby controls theinjection quantity of the fuel injection valves 21 and the ignitiontiming of the spark plugs 22 in accordance with the state of engineoperation.

The ECU 28 executes a variable intake valve control program and therebyswitches the control mode of the variable intake valve lifters 30between low lift mode and high lift mode in accordance with the state ofengine operation. In low lift mode, as illustrated in FIG. 2, the ECU 28reduces the amount of lift of the intake valve 29 and reduces a valveopening duration. In high lift mode, as illustrated in FIG. 3, the ECU28 increases the amount of lift of the intake valves 29 and increases avalve opening duration.

To reduce the likelihood of a rich or lean spike, the ECU 28 executes afuel injection timing computation program. Generally, when the amount oflift of the intake valve is varied (e.g., switching from high lift tolow lift mode or from low lift to high lift mode) the fuel injectiontiming computation program corrects and varies fuel injectiontermination timing according to the variation of the lift of the intakevalve. For instance, when the variable intake valve lifter 30 isswitched from low lift mode to high lift mode and the amount of lift ofan intake valve 29 is increased, the fuel injection termination timingis corrected and advanced. Also, when a variable intake valve lifter 30is switched from high lift mode to low lift mode and the amount of liftof an intake valve 29 is reduced, the fuel injection termination timingis corrected and delayed.

When the fuel injection termination timing is corrected and advanced,the mixing time for injected fuel and intake air is accordinglyincreased, and the air-fuel ratio distribution of fuel mixture in thecylinder can be made uniform. Therefore, when the amount of lift of theintake valve 29 is increased, the fuel injection termination timing iscorrected and advanced to make the air-fuel ratio distribution of fuelmixture in the cylinder more uniform. Also, even though the valveclosing timing of the intake valve 29 is delayed more and the back flowof fuel mixture in the cylinder is increased, the average air-fuel ratioin the cylinder can be kept substantially constant. As a result, theoccurrence of a lean spike is less likely.

When the fuel injection termination timing is corrected and delayed, thequantity of injected fuel sticking to the intake valve 29 is increased.Thus, the quantity of fuel sucked into the cylinder can be reduced.Therefore, when the amount of lift of an intake valve 29 is reduced, thefuel injection termination timing is corrected and delayed to reduce thequantity of fuel sucked into the cylinder. Thus, even though the valveclosing timing of the intake valve 29 is advanced and the back flow ofrich gas in the cylinder is reduced (i.e., the residual volume of richgas in the cylinder is increased), the average air-fuel ratio in thecylinder can be kept substantially constant. As a result, the occurrenceof a rich spike is less likely.

Hereafter, description will be given to the details of the processing ofthe fuel injection timing computation program executed by the ECU 28 asillustrated in FIG. 4. The fuel injection timing computation programillustrated in FIG. 4 is executed at predetermined intervals while theengine is in operation. When the program is started, the current amountof lift of the intake valve is computed at Step S101, and the currentvalve closing timing of the intake valve is computed at Step S102.

Thereafter, the ECU proceeds to Step S103, and computes a basicinjection quantity based on the current intake air quantity and thetarget air-fuel ratio using a map, a mathematical expression, or thelike. Thereafter, the ECU proceeds to Step S104, and computes basic fuelinjection termination timing based on the current engine revolutionspeed and quantity of air filled in cylinder. (The basic fuel injectiontermination timing is time delayed behind the time of initiation ofbasic fuel injection by a fuel injection time.)

At Step S105, thereafter, the ECU determines whether or not a variationin the amount of lift of the intake valve is equal to or larger than apredetermined value. The variation in the amount of lift is, forexample, the difference between the current amount of lift of the intakevalve and the previous amount of lift of the intake valve. Next, in StepS106, the ECU determines whether or not a variation in the valve closingtiming of the intake valve is equal to or lager than a predeterminedvalue. The variation in the valve closing timing is, for example, thedifference between the current valve closing timing of the intake valveand the previous valve closing timing of the intake valve.

In cases where the ECU determines that the variation in the amount oflift of the intake valve is greater than or equal to the predeterminedvalue at Step 105 and that the variation in the valve closing timing ofthe intake valve is greater than or equal to the predetermined value atStep S106, the ECU determines that the control mode of the variableintake valve lifter 30 has been switched. Then, in Step S107 the ECUcomputes an amount of correction, A, for the fuel injection terminationtiming based on the valve closing timing of the intake valve using amap, a mathematical expression, or the like.

The amount of correction, A, is set such that, when the variable intakevalve lifter 30 is switched from low lift mode to high lift mode and thevalve closing timing of the intake valve is delayed more, the fuelinjection termination timing is corrected and advanced. In other words,when the amount of lift of the intake valve is varied and the valveclosing timing of the intake valve is delayed more, the fuel injectiontermination timing is corrected and advanced. Also, when the variableintake valve lifter 30 is switched from high lift mode to low lift modeand the valve closing timing of the intake valve is advanced, the fuelinjection termination timing is corrected and delayed. In other words,when the amount of lift of the intake valve is reduced and the valveclosing timing of the intake valve is advanced, the fuel injectiontermination timing is corrected and delayed.

After the computation of the amount of correction, A, the ECU proceedsto Step S108 to obtain a final fuel injection termination timing.Specifically, the ECU corrects the basic fuel injection termination byadding the correction amount, A, to the basic fuel injection terminationtiming to compute the final fuel injection termination timing (i.e.,Final Fuel Injection Termination Timing=Basic Fuel Injection TerminationTiming+A).

Thus, when the variable intake valve lifter 30 is switched from low liftmode to high lift mode to increase the amount of lift of the intakevalve, the fuel injection termination timing is corrected and advanced.Also, when the variable intake valve lifter 30 is switched from highlift mode to low lift mode to reduce the amount of lift of the intakevalve 29, the fuel injection termination timing is corrected anddelayed.

In cases where the ECU determines that the variation in the amount oflift of the intake valve is smaller than the predetermined value at StepS105, or in cases where the ECU determines that the variation in thevalve closing timing of the intake valve is smaller than thepredetermined value at Step S106, the ECU determines that the currentcontrol mode of the variable intake valve lifter 30 is maintained, andStep S109 follows. In Step S109, the ECU sets the basic fuel injectiontermination timing, computed at Step S104, as the final fuel injectiontermination timing (i.e., Final Fuel Injection Termination Timing=BasicFuel Injection Termination Timing).

In summary, when the variable intake valve lifter 30 is switched fromlow lift mode to high lift mode to increase the amount of lift of theintake valve 29, the fuel injection termination timing is corrected andadvanced to make the air-fuel ratio distribution of fuel mixture in thecylinder more uniform. Therefore, even though the valve closing timingof the intake valve 29 is delayed and the back flow of fuel mixture inthe cylinder is increased, the average air-fuel ratio in the cylindercan be kept substantially constant. Thus, when the amount of lift of theintake valve 29 is increased, the occurrence of a lean spike is lesslikely. As a result, torque shock due to a lean spike is less likely,drivability is enhanced, and exhaust emissions are improved.

Meanwhile, when the variable intake valve lifter 30 is switched fromhigh lift mode to low lift mode to reduce the amount of lift of theintake valve 29, the fuel injection termination timing is corrected anddelayed. The quantity of fuel sucked into the cylinder is therebyreduced. Therefore, even though the valve closing timing of the intakevalve 29 is advanced, and the back flow of rich gas in the cylinder isreduced (i.e., the residual volume of rich gas in the cylinder isincreased), the average air-fuel ratio in the cylinder can be keptsubstantially constant. Thus, when the amount of lift of the intakevalve 29 is reduced, the occurrence of a rich spike is less likely. As aresult, torque shock due to a rich spike is less likely, drivability isenhanced, and exhaust emissions are improved.

Second Embodiment

Next, description will be given to the second embodiment of theinvention with reference to FIG. 5. Generally, when the variable intakevalve lifter 30 is switched from low lift mode to high lift mode toincrease the amount of lift of the intake valve 29, the injectionquantity is corrected and increased to reduce the likelihood of a leanspike. Also, when the variable intake valve lifter 30 is switched fromhigh lift mode to low lift mode to reduce the amount of lift of theintake valve 29, the injection quantity is corrected and reduced toreduce the likelihood of a rich spike.

The injection quantity computation program illustrated in FIG. 5 isexecuted at predetermined intervals while the engine is in operation.When the program is started, the current amount of lift of the intakevalve is computed in Step S201, and the current valve closing timing ofthe intake valve is computed in step S202. Then in Step S203, the ECUcomputes a basic injection quantity based on the current intake airquantity and a target air-fuel ratio.

Next in Step S204, the ECU determines whether or not a variation in theamount of lift of the intake valve greater than or equal to apredetermined value. In the next Step S205, the ECU determines whetheror not a variation in the valve closing timing of the intake valve isgreater than or equal to a predetermined value.

In cases where the ECU determines that the variation in the amount oflift of the intake valve is greater than or equal to the predeterminedvalue at Step S204 and that the variation in the valve closing timing ofthe intake valve is greater than or equal to the predetermined value atStep S205, the ECU determines that the control mode of the variableintake valve lifter 30 has been switched. Then in Step S206, the ECUprohibits purge control such that evaporative gas, produced by fuel inthe fuel tank being evaporated, is not purged into the air intake systemof the engine 11.

Thereafter, the ECU proceeds to Step S207, and computes a fuelcorrection factor α based on the variation in the valve closing timingof the intake valve using a map, a mathematical expression, or the like.Thereafter, the ECU proceeds to Step S208 and computes a fuel correctionfactor β based on the variation in the amount of lift of the intakevalve using a map, a mathematical expression, or the like.

In this map of fuel correction factor α and map of fuel correctionfactor β, the fuel correction factor α and the fuel correction factor βare set so that, when the variable intake valve lifter 30 is switchedfrom low lift mode to high lift mode and the valve closing timing of theintake valve is delayed, the back flow of rich gas in the cylinder isincreased (i.e., the residual volume of rich gas in the cylinder isreduced). In other words, when the amount of lift of the intake valve isincreased and the valve closing timing of the intake valve is delayed,the back flow of rich gas in the cylinder is increased. Therefore, theinjection quantity is corrected and accordingly increased. Also, whenthe variable intake valve lifter 30 is switched from high lift mode tolow lift mode and the valve closing timing of the intake valve isadvanced, the back flow of rich gas in the cylinder is reduced (i.e.,the residual volume of rich gas in the cylinder is increased). In otherwords, when the amount of lift of the intake valve is reduced and thevalve closing timing of the intake valve is advanced, the back flow ofrich gas in the cylinder is reduced. Therefore, the injection quantityis corrected and accordingly reduced.

After the computation of fuel correction factor α and fuel correctionfactor β, the ECU proceeds to Step S209. Specifically, the ECU correctsthe basic injection quantity and computes a final injection quantity bymultiplying the basic injection quantity by the fuel correction factor,α, and the fuel correction factor, β (i.e., Final Injection QuantityBasic Injection Quantity×Fuel Correction Factor α×Fuel Correction Factorβ).

Thus, when the variable intake valve lifter 30 is switched from low liftmode to high lift mode to increase the amount of lift of the intakevalve, the injection quantity is corrected and increased. Also, when thevariable intake valve lifter 30 is switched from high lift mode to lowlift mode to reduce the amount of lift of the intake valve 29, theinjection quantity is corrected and reduced.

In cases where the ECU determines that the variation in the amount oflift of the intake valve is less than the predetermined value at StepS204, or in cases where the ECU determines that the variation in thevalve closing timing of the intake valve is less than the predeterminedvalue at Step S205, Step S210 follows. Specifically, the ECU determinesthat the current control mode of the variable intake valve lifter 30 ismaintained, and the ECU sets the basic injection quantity, computed atStep S203, as final injection quantity (i.e., Final InjectionQuantity=Basic Injection Quantity).

Thus, when the variable intake valve lifter 30 is switched from low liftmode to high lift mode to increase the amount of lift of the intakevalve 29, the injection quantity is corrected and increased. Therefore,even though the amount of lift of the intake valve 29 is increased, thevalve closing timing of the intake valve 29 is delayed, and the backflow of rich gas in the cylinder is increased (i.e., the residual volumeof rich gas in the cylinder is reduced), the injection quantity can becorrected and accordingly increased to increase the quantity of fuelsucked into the cylinder. Also, the average air-fuel ratio in thecylinder can be kept substantially constant. Thus, when the amount oflift of the intake valve 29 is increased, a lean spike is less likely,drivability is improved, and the exhaust emission is also improved.

Meanwhile, when the variable intake valve lifter 30 is switched fromhigh lift mode to low lift mode to reduce the amount of lift of theintake valve 29, the injection quantity is corrected and reduced.Therefore, even though the amount of lift of the intake valve 29 isreduced, the valve closing timing of the intake valve 29 is advanced,and the back flow of rich gas in the cylinder is reduced (i.e., theresidual volume of rich gas in the cylinder is increased), the injectionquantity can be corrected and accordingly reduced to reduce the quantityof fuel sucked into the cylinder. Also, the average air-fuel ratio inthe cylinder can be kept substantially constant. Thus, when the amountof lift of the intake valve 29 is reduced, a rich spike is less likely,the drivability is improved, and the exhaust emission is also improved.

When the amount of lift of the intake valve 29 is varied, a variation(i.e., increment or decrement) in the back flow of rich gas in acylinder changes in accordance with a variation in the valve closingtiming of the intake valve 29. In the second embodiment, this change istaken into account, and when the amount of lift of the intake valve 29is varied, a fuel correction factor, α, is set based on a variation inthe valve closing timing of the intake valve 29. Therefore, it ispossible to appropriately set a fuel correction factor, α, in accordancewith a change (i.e., increment or decrement) in variation in the backflow of rich gas corresponding to a variation in the valve closingtiming of the intake valve 29. As a result, the occurrence of a leanspike or a rich spike is less likely.

Furthermore in this embodiment, when the amount of lift of the intakevalve 29 is varied, purge control is prohibited. Therefore, externaldisturbance to the air-fuel ratio can be avoided when the amount of liftof the intake valve is varied. Thus, it is possible to enhance theaccuracy of controlling the air-fuel ratio of fuel mixture when theamount of lift of an intake valve is varied, and the occurrence of alean spike or a rich spike is even less likely.

Third Embodiment

Description will be given to the third embodiment of the invention withreference to FIG. 6 and FIG. 7.

As illustrated in FIG. 6, the engine 11 is a four-valve engine havingfour valves for each cylinder. Each cylinder is provided with two intakeports 31 and two exhaust ports 32. Each intake port 31 is provided withan intake valve 29, and each exhaust port 32 is provided with an exhaustvalve 33.

A swirl valve 34 (i.e., a swirl flow generating device) is included ineither of the two intake ports 31 of the cylinder. The swirl valve 34generates a swirl flow in the corresponding cylinder. The swirl valve 34of each cylinder is so constructed that it is driven and opened/closedby a motor or the like (not shown). The ECU 28 executes the swirl valvecontrol program illustrated in FIG. 7. As such, when the engine is in apredetermined operating range (e.g. low-revolution, low-load operatingrange, etc.), the swirl valve 34 is closed to generate a swirl flow inthe cylinder.

Hereafter, description will be given to the details of the processing ofthe swirl valve control program carried out by the ECU 28 in the thirdembodiment, with reference to FIG. 7. The swirl valve control programillustrated in FIG. 7 is executed at predetermined intervals while theengine is in operation. When the program is started, the current enginerevolution speed is computed at Step S301. At the next step, Step S302,the current quantity of air filled in cylinder is computed.

Thereafter, the ECU proceeds to Step S303 wherein a basic injectionquantity is computed based on the current engine revolution speed andquantity of air filled in cylinder using a map, a mathematicalexpression, or the like. Thereafter, the ECU proceeds to Step S304, andcomputes a basic fuel injection termination timing based on the currentengine revolution speed and quantity of air filled in cylinder. (Thebasic fuel injection termination timing is time delayed behind the timeof initiation of basic fuel injection by a fuel injection time.)

At Step S305, thereafter, the ECU determines whether or not the engineis in a low-revolution operating range according to whether the enginerevolution speed is less than or equal to a predetermined value. At thenext step, or Step S306, it determines whether or not the engine is in alow-load operating range according to whether the quantity of air filledin cylinder is less than or equal to a predetermined value.

In cases where the ECU determines that the engine is in a low-revolutionoperating range at Step S305 and that the engine is in a low-loadoperating range at Step S306, Step S307 follows, and the swirl valve 34of each cylinder is closed. As such, intake air is let into eachcylinder through only either of the two intake ports 31 of the cylinderto generate a swirl flow in the cylinder. The air-fuel ratiodistribution of fuel mixture in the cylinder is thereby made moreuniform.

In cases where the ECU determines the engine is in a high-revolutionoperating range at Step S305 or that the engine is in a high-loadoperating range at Step S306, Step S308 follows, and the swirl valve 34is opened for each cylinder. As such, intake air is let into eachcylinder through the two intake ports 31 of the cylinder, and asufficient quantity of air filled in cylinder is ensured.

Thus, when the engine is in a predetermined engine operating range (e.g.low-revolution, low-load operating range), a swirl valve 34 is closed togenerate a swirl flow in the relevant cylinder, and the air-fuel ratiodistribution of fuel mixture in the cylinder is thereby made moreuniform. Therefore, in this engine operating range (i.e., an operatingrange in which the air-fuel ratio distribution of fuel mixture in eachcylinder is made more uniform by a swirl flow), even though the amountof lift of the intake valve 29 is varied by the variable intake valvelifter 30 and the valve closing timing of the intake valve 29 is delayedor advanced to increase or reduce the back flow of fuel mixture in thecylinder, the average air-fuel ratio in the cylinder can be keptsubstantially constant. Thus, when the amount of lift of the intakevalve is varied, the occurrence of a lean spike or a rich spike is lesslikely, thereby improving the drivability and the exhaust emission.

Fourth Embodiment

Description will be given to the fourth embodiment of the invention withreference to FIG. 8 and FIG. 9.

In the fourth embodiment, a variable valve timing mechanism (not shown)is provided which is capable of varying the valve timing(opening/closing timing) of the intake valve 29 at high speed by a motoror the like. When the amount of lift of the intake valve 29 is varied bythe variable intake valve lifter 30, the variable valve timing mechanismis so controlled that the valve closing timing of the intake valve 29 isnot changed.

More specific description will be given. When the variable intake valvelifter 30 is switched from low lift mode to high lift mode to increasethe amount of lift of the intake valve 29, as illustrated in FIG. 8, thevalve timing of the intake valve 29 is instantaneously advanced by thevariable valve timing mechanism. As such, the valve closing timing ofthe intake valve 29 remains constant. Thereafter, the valve timing ofthe intake valve 29 is gradually delayed by the variable valve timingmechanism to return the valve closing timing of the intake valve 29 tothe normal valve closing timing in high lift mode.

When the variable intake valve lifter 30 is switched from high lift modeto low lift mode to reduce the amount of lift of the intake valve 29, asillustrated in FIG. 9, the valve timing of the intake valve 29 isinstantaneously delayed by the variable valve timing mechanism. As such,the valve closing timing of the intake valve 29 is not changed.Thereafter, the valve timing of the intake valve 29 is graduallyadvanced by the variable valve timing mechanism to return the valveclosing timing of the intake valve 29 to the normal valve closing timingin low lift mode.

Thus, when variable intake valve lifter 30 varies the amount of lift ofthe intake valve 29, the variable valve timing mechanism is controlledso that the valve closing timing of the intake valve 29 remainsapproximately constant. Therefore, when the amount of lift of the intakevalve is varied, the back flow of rich gas in the cylinder can remainapproximately constant, and the average air-fuel ratio in the cylindercan remain substantially constant. Accordingly, when the amount of liftof the intake valve is varied, the occurrence of a lean spike or a richspike is unlikely to thereby improve the drivability and the exhaustemission.

In the first to fourth embodiments mentioned above, a system is equippedwith a variable intake valve lifter that performs switching between lowlift mode and high lift mode and thereby instantaneously varies theamount of lift of an intake valve. The invention is not limited to theseembodiments. For instance, it may be applied to systems that areequipped with a variable intake valve lifter that continuously variesthe amount of lift of an intake valve by a motor or the like. It mayalso be applied to an electromagnetically driven intake valve, and thelike, and in which the amount of lift of the intake valve can beinstantaneously varied.

While only the selected preferred embodiments have been chosen toillustrate the present invention, it will be apparent to those skilledin the art from this disclosure that various changes and modificationscan be made therein without departing from the scope of the invention asdefined in the appended claims. Furthermore, the foregoing descriptionof the preferred embodiments according to the present invention isprovided for illustration only, and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

1. A control apparatus for an internal combustion engine that varies theamount of lift of an intake valve, the control apparatus comprising: afuel injection timing correcting device that, when the amount of lift ofthe intake valve is varied, corrects and varies fuel injectiontermination timing according to the variation of the lift of the intakevalve.
 2. The control apparatus according to claim 1, wherein the fuelinjection timing correcting device corrects and advances fuel injectiontermination timing when the amount of lift of the intake valve isincreased.
 3. The control apparatus according to claim 1, wherein thefuel injection timing correcting device corrects and delays fuelinjection termination timing when the amount of lift of the intake valveis reduced.
 4. A control apparatus for an internal combustion enginethat varies the amount of lift of an intake valve for a cylinder, thecontrol apparatus comprising: a swirl flow generating device thatgenerates a swirl flow in the cylinder.
 5. A control apparatus for aninternal combustion engine equipped with a variable intake valve lifterthat varies the amount of lift of an intake valve and a variable valvetiming mechanism that varies the opening/closing timing of the intakevalve, the control apparatus comprising: an intake valve closing timingcorrecting device that, when the amount of lift of the intake valve isvaried by the variable intake valve lifter, controls the variable valvetiming mechanism so that the valve closing timing of the intake valveremains substantially constant.
 6. A control apparatus for an internalcombustion engine that varies the amount of lift of an intake valve, thecontrol apparatus comprising: an injection quantity correcting devicethat, when the amount of lift of the intake valve is varied, correctsand varies an injection quantity.
 7. A control apparatus according toclaim 6, wherein the injection quantity correcting device corrects andincreases an injection quantity when the amount of lift of the intakevalve is increased by the variable intake valve lifter.
 8. A controlapparatus according to claim 6, wherein the injection quantitycorrecting device corrects and reduces an injection quantity when theamount of lift of the intake valve is reduced by the variable intakevalve lifter.
 9. The control apparatus according to claim 6, wherein theinjection quantity correcting device sets an amount of correction forinjection quantity based on a variation in the valve closing timing ofthe intake valve when the amount of lift of the intake valve is varied.10. The control apparatus according to claim 6, further comprising anevaporative gas purge prohibiting device that, when the amount of liftof the intake valve is varied, prohibits purge of evaporative gas intothe air intake system.
 11. A method of controlling fuel injection timingfor an internal combustion engine that varies the amount of lift of anintake valve, the method comprising: correcting and varying fuelinjection termination timing according to the variation of the lift ofthe intake valve when the amount of lift of the intake valve is varied.12. The method of claim 11, wherein the correcting and varying comprisescorrecting and advancing fuel injection termination timing when theamount of lift of the intake valve is increased.
 13. The method of claim11, wherein the correcting and varying comprises correcting and delayingfuel injection termination timing when the amount of lift of the intakevalve is reduced.
 14. A method of controlling opening/closing timing ofan intake valve of an internal combustion engine equipped with avariable intake valve lifter that varies the amount of lift of an intakevalve and a variable valve timing mechanism that varies theopening/closing timing of the intake valve, the method comprising:controlling the variable valve timing mechanism so that the valveclosing timing of the intake valve remains substantially constant whenthe amount of lift of the intake valve is varied by the variable intakevalve lifter.
 15. A method of controlling an injection quantity of anintake valve of an internal combustion engine that varies the amount oflift of the intake valve, the method comprising: correcting and varyingan injection quantity when the amount of lift of the intake valve isvaried.
 16. The method according to claim 15, wherein the correcting andvarying comprises correcting and increasing an injection quantity whenthe amount of lift of the intake valve is increased by the variableintake valve lifter.
 17. The method according to claim 15, wherein thecorrecting and varying comprises correcting and reducing an injectionquantity when the amount of lift of the intake valve is reduced by thevariable intake valve lifter.
 18. The method according to claim 15,further comprising setting an amount of correction for injectionquantity based on a variation in the valve closing timing of the intakevalve when the amount of lift of the intake valve is varied.
 19. Themethod according to claim 15, further comprising prohibiting purge ofevaporative gas into the air intake system when the amount of lift ofthe intake valve is varied.